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SubjectRe: [PATCH net-next 3/3] tap: XDP support
On Fri, Jul 28, 2017 at 11:28:54AM +0800, Jason Wang wrote:
> > > + old_prog = rtnl_dereference(tun->xdp_prog);
> > > + if (old_prog)
> > > + bpf_prog_put(old_prog);
> > > + rcu_assign_pointer(tun->xdp_prog, prog);
> > Is this OK? Could this lead to the program getting freed and then
> > datapath accessing a stale pointer? I mean in the scenario where the
> > process gets pre-empted between the bpf_prog_put() and
> > rcu_assign_pointer()?
>
> Will call bpf_prog_put() after rcu_assign_pointer().

I suspect you need to sync RCU or something before that.

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